Gecko

Also known as Gecko engine, Gecko rendering engine, Firefox Gecko, Mozilla Gecko

free HTML layout engine

Key facts

Original author: Netscape
Developers: Mozilla Foundation , Mozilla Corporation , Adobe Systems , and other contributors
Initial release: 1998 as NGLayout
Stable release: 125 / 16 February 2026 ; 3 months ago ( 16 February 2026 )
Written in: C++ , JavaScript , Rust
Type: Browser engine
License: MPL 2.0
Website: developer .mozilla .org /en-US /docs /Glossary /Gecko
Repository: hg .mozilla .org /mozilla-central /

via Wikipedia infobox

Official website

Gecko - Glossary | MDN

Gecko is the layout engine developed by the Mozilla Project and used in many apps/devices, including Firefox and Firefox OS.

~13 min read

Article

Gecko is a browser engine developed by Mozilla. It is used in the Firefox browser, the Thunderbird email client, and in a discontinued state on AOL's Netscape 6, Netscape 7, Netscape Browser and Netscape Navigator 9; this is alongside many other projects.

Gecko is designed to support open Internet standards, and is used by different applications to display web pages and, in some cases, an application's user interface itself (by rendering XUL). Gecko offers a rich programming API that makes it suitable for a wide variety of roles in Internet-enabled applications, such as web browsers, content presentation, and client/server.